1. Field of the Invention
The present invention relates to antenna arrays and, more particularly, is directed to low-cost antenna arrays and methods of manufacturing antenna arrays having substantially planar and curved surfaces for telecommunications applications.
2. Description of the Related Art
Antenna arrays have been manufactured in a variety of forms and have many different applications in the communications field. One particular application with a high volume and an emphasis on cost of the antenna arrays is for use in base-stations of mobile communication systems, such as cellular transmissions operating at about 800 MHz and Personal Communication Services (PCS) transmissions operating at about 1900 MHz in the United States, as well as other wireless and mobile communication applications worldwide.
Base-station antenna arrays have been formed using a wide variety of structures having significant variations in size, cost and reliability. Conventional base-station antenna arrays typically include two or more individual radiators, a transmission network to distribute RF power among the radiators from an interface port of the antenna, a mechanical structure securing all the elements into an assembly, and a protective radome. One basic type of base-station antenna array is formed from a known array of cylindrical dipoles. These antenna arrays generally have a large number of components, a high cost for manufacturing the structures, large physical size and a relatively heavy weight. Another basic type of base-station antenna array is formed using sheet metal dipole radiators and a micro-strip power distribution network formed from sheet metal supported by discrete dielectric spacers. The individual metal parts are typically stamped from aluminum sheet stock and then assembled in a labor-intensive operation. Another conventional base-station antenna array uses printed circuit boards (PCB's) for power dividing circuits and metal dipole or patch radiators interconnected using coaxial cables.
Another type of conventional base-station antenna array uses PCB's for the power distribution network and separate PCB's for the dipole radiators. For base station antennas with high gain values and having greater than eight radiators it is generally necessary to use high performance polytetrafluoroethylene (PTFE) based PCB materials for the power distribution network for maintaining low network losses due to signal dissipation. High performance PTFE based PCB materials have a significantly higher cost compared to other types of PCB materials. Base-station antennas constructed using PCB's for the power distribution network and for the radiators can offer advantages over similar antennas constructed using sheet metal with regard to manufacturing tooling costs, reproduction, ease of assembly, and can facilitate greater circuit complexity.
Planar antenna arrays of various constructions have been proposed to decrease the cost of manufacturing, the physical size and weight of the resulting antenna arrays. These arrays have been formed in various structures utilizing a variety of sandwich type arrangements and with various types of materials for the antenna radiators and circuitry. Planar antenna arrays have conventionally been formed by screen-printing, by physically cutting a metal layer, such as by punching out radiator patches or by cutting the metal to form the radiator patches in the metal layer, and by etching of the metal layer to form the desired pattern. These types of antennas have included one or more circuits and radiators formed of very thin metallic layers or foils which then are supported or mounted on various types of generally rigid dielectric substrates, such as plastic, foam, Styrofoam™, PVC resin, fiberglass, polypropylene, polyester, acrylic or polyethylene. While these conventional array structures have improved some characteristics of antenna arrays, such as the number of components and weight, the electrical performance, the cost of the manufacturing process and the resulting mechanical structures need to be improved.
Accordingly, there is a need for an antenna array, that may be used, for example, in base-station applications, which can be manufactured at a reduced cost. It also would be desirable to attain the desired reduced cost of the arrays while maintaining acceptable electrical performance of the antenna array. It would further be desirable to form a flexible antenna array, which can have a curved structure for certain applications.